1. Technical Field
The present disclosure relates to adaptive control of exhaust gas recirculation (EGR) for internal combustion engines.
2. Background Art
Exhaust gas recirculation (EGR) is a well known technique used in various types of internal combustion engines to reduce NOx generation during combustion. To control EGR flow, external EGR systems typically use either a linear solenoid or DC motor to change the EGR valve position with feedback provided by a position sensor for closed loop control. To provide a desired EGR mass flow rate into the engine intake system, the valve position is changed with the corresponding position sensor voltage stored in a look-up table or map over a range of engine speed/load or torque during vehicle system development. However, as the EGR flow degrades during actual operation due to deposit build-up in the EGR valve, EGR cooler, and/or associated piping, the previously stored map or look-up table representing the relationship between the position sensor voltage and EGR mass flow rate becomes less accurate. While various strategies have been developed to measure or estimate actual EGR flow, many require additional sensors that increase cost and complexity and may present challenges for reliability and durability due to the harsh operating environment within the EGR passages. In addition, many EGR control strategies are difficult to incorporate or retrofit into existing systems.